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        <td class="header">&nbsp; Azimuth Filtering (InSAR operator)</td>
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<h3>Azimuth Filtering</h3>

<p>
    This operator filters the spectras, of stack of SLC images, in the azimuth direction. This is an
    optional step in the interferometric processing chain.
    The part of the spectras do that does not overlap with the spectrum of the slave is filtered out. This
    non overlap is due to the selection of a Doppler centroid frequency in the SAR processing, which normally is
    not equal for master and slave image.
</p>

<p>
    This step can in general best be performed after the coregistration. (The offset in range direction is used to
    evaluate the polynomial for the Doppler Centroid frequency.)
</p>

<p>
    Operator performs filtering of all images in the stack at the same time. However, if multiple slave images are
    present in the stack, only slave images will be filtered, and master image will remain unfiltered (all slaves
    coregistered on the same master image). This approach has the advantage that for each interferogram of the stack
    a separate set of master images is created, effectively saving the disk storage space and making the processing
    more efficient. The disadvantage of not filtering the master is that a small part of the spectrum of the master
    is not shared with the slave spectrum, yielding a minor loss of coherence in the interferogram.
</p>

<h4>Operator parameters:</h4>&nbsp;&nbsp;

<ul>
    <li>
        <b>FFT Window Length:</b> Length of FFT estimation window per tile in azimuth direction. In general, the larger the
        better. However, not that if the value for the FFT Window Lenght is larger then the size of Tile, the length of
        the window will be reduced to the maximum possible length.
    </li>
    <li>
        <b>Azimuth Filter Overlap:</b> Half of the overlap between consecutive tiles in azimuth
        direction. Partially the same data is used to estimate the spectrum, to avoid border effects.
        However, the exact influence of this parameter to the end results scales with the Doppler Centroid Frequency
        variability between master and slave images. It has not been studied yet, what is the optimum ratio between
        Overlap parameter and Doppler Centroid Frequency difference. Setting this card to 0 gives the fastest results.
    </li>
    <li>
        <b>Hamming Alpha:</b> The weighting of the spectrum in azimuth direction. The filtered output spectrum is first
        de-weighted with the specified hamming filter, then re-weighted with a (newly centered) one. If this
        parameter is set to 1, no weighting is performed.
    </li>
</ul>

<h4>Source bands:</h4>&nbsp;&nbsp;
<p> Source Bands are set of coregistered bands of the complex product.</p>

<h4>Output bands:</h4>&nbsp;&nbsp;
<p> Output Bands are set of bands with spectras filtered in azimuth direction.</p>


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